Derivatives and Risk Management (Balance Sheet Classification of Derivative Financial Instruments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative assets	$ 391	$ 191
Derivative liabilities	236	139
Not Designated as Hedging Instrument | Interest rate swap | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	0	1
Natural Gas | Fixed Price Swaps
Derivatives, Fair Value [Line Items]
Premium paid	9
Natural Gas | Not Designated as Hedging Instrument | Fixed Price Swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	77	32
Premium paid	9
Natural Gas | Not Designated as Hedging Instrument | Fixed Price Swaps | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	7	6
Natural Gas | Not Designated as Hedging Instrument | Fixed Price Swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	1	9
Natural Gas | Not Designated as Hedging Instrument | Fixed Price Swaps | Derivative liabilities | Purchased
Derivatives, Fair Value [Line Items]
Derivative liabilities	1	0
Natural Gas | Not Designated as Hedging Instrument | Fixed Price Swaps | Other long-term liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	0	1
Natural Gas | Not Designated as Hedging Instrument | Two-Way Costless Collars | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	10	11
Natural Gas | Not Designated as Hedging Instrument | Two-Way Costless Collars | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	4	0
Natural Gas | Not Designated as Hedging Instrument | Two-Way Costless Collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	4	7
Natural Gas | Not Designated as Hedging Instrument | Two-Way Costless Collars | Other long-term liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	4	0
Natural Gas | Not Designated as Hedging Instrument | Three-Way Costless Collars | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	126	41
Natural Gas | Not Designated as Hedging Instrument | Three-Way Costless Collars | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	74	34
Natural Gas | Not Designated as Hedging Instrument | Three-Way Costless Collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	84	33
Natural Gas | Not Designated as Hedging Instrument | Three-Way Costless Collars | Other long-term liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	72	35
Natural Gas | Not Designated as Hedging Instrument | Basis swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	17	8
Natural Gas | Not Designated as Hedging Instrument | Basis swaps | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	15	3
Natural Gas | Not Designated as Hedging Instrument | Basis swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	17	18
Natural Gas | Not Designated as Hedging Instrument | Basis swaps | Other long-term liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	9	4
Natural Gas | Not Designated as Hedging Instrument | Call Option | Derivative assets | Purchased
Derivatives, Fair Value [Line Items]
Derivative assets	1	0
Natural Gas | Not Designated as Hedging Instrument | Call Option | Other long-term assets | Purchased
Derivatives, Fair Value [Line Items]
Derivative assets	2	6
Natural Gas | Not Designated as Hedging Instrument | Call Option | Derivative liabilities | Sold
Derivatives, Fair Value [Line Items]
Derivative liabilities	3	3
Natural Gas | Not Designated as Hedging Instrument | Call Option | Other long-term liabilities | Sold
Derivatives, Fair Value [Line Items]
Derivative liabilities	15	19
Oil | Not Designated as Hedging Instrument | Fixed Price Swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	4	13
Oil | Not Designated as Hedging Instrument | Fixed Price Swaps | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	1	6
Oil | Not Designated as Hedging Instrument | Fixed Price Swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	6	0
Oil | Not Designated as Hedging Instrument | Fixed Price Swaps | Derivative liabilities | Purchased
Derivatives, Fair Value [Line Items]
Derivative liabilities	0	6
Oil | Not Designated as Hedging Instrument | Fixed Price Swaps | Other long-term liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	2	0
Oil | Not Designated as Hedging Instrument | Two-Way Costless Collars | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	5	6
Oil | Not Designated as Hedging Instrument | Two-Way Costless Collars | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	0	5
Oil | Not Designated as Hedging Instrument | Two-Way Costless Collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	5	0
Oil | Not Designated as Hedging Instrument | Two-Way Costless Collars | Other long-term liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	0	1
Oil | Not Designated as Hedging Instrument | Three-Way Costless Collars | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	3	0
Oil | Not Designated as Hedging Instrument | Three-Way Costless Collars | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	7	0
Oil | Not Designated as Hedging Instrument | Three-Way Costless Collars | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	4	0
Oil | Not Designated as Hedging Instrument | Three-Way Costless Collars | Other long-term liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	8	0
Oil | Not Designated as Hedging Instrument | Call Option | Other long-term liabilities | Sold
Derivatives, Fair Value [Line Items]
Derivative liabilities	1	0
Propane | Not Designated as Hedging Instrument | Fixed Price Swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	21	11
Propane | Not Designated as Hedging Instrument | Fixed Price Swaps | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	3	0
Propane | Not Designated as Hedging Instrument | Two-Way Costless Collars | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	2	0
Ethane | Not Designated as Hedging Instrument | Fixed Price Swaps | Derivative assets
Derivatives, Fair Value [Line Items]
Derivative assets	11	7
Ethane | Not Designated as Hedging Instrument | Fixed Price Swaps | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	0	1
Ethane | Not Designated as Hedging Instrument | Fixed Price Swaps | Derivative liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	0	3
Natural gas storage | Not Designated as Hedging Instrument | Fixed Price Swaps | Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	$ 1	$ 0